Re: chromatic aberration

Posted by Guy Cox-2 on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Concentrating-bacteria-cells-for-microscope-visualization-tp6519025p7134557.html

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The CA you mention seems quite extreme for an NA 0.4 objective, but you need to define what you mean by far red.  I think the red wavelength usually used for the third correction point is 646nm.  Some apochromats can diverge quite sharply beyond this point, so if your 'far-red' is 700nm then you are beyond the correction range of the objective and have no grounds for complaint.  Some modern apos are violet corrected and will therefore probably be even worse at long wavelengths - but this should be marked on the lens.  Some apos are marked IR but I'm not sure if that implies chromatic correction into the IR or just good transmission.  

If you get a 2.5µm focal shift between 486 (blue) and 646 (red) then you should demand a replacement from the manufacturer.  

                                        Guy

Optical Imaging Techniques in Cell Biology
by Guy Cox    CRC Press / Taylor & Francis
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-----Original Message-----
From: Confocal Microscopy List [mailto:[hidden email]] On Behalf Of MODEL, MICHAEL
Sent: Thursday, 29 December 2011 8:36 AM
To: [hidden email]
Subject: Re: chromatic aberration

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I use fluorescent multicolor beads on a coverslip. But even before, I have noticed that when I am looking at cells in transmission, I see different things depending on the filter. You may argue that with cells, there is spherical aberration, etc but with beads there shouldn't be any. So I thought that perhaps low-NA objectives are generally less well corrected for longitudinal chromatic aberration? Even when of the planapo type. Olympus does not provide any numbers, just says that the objectives are 'excellent".

-----Original Message-----
From: Confocal Microscopy List [mailto:[hidden email]] On Behalf Of Martin Wessendorf
Sent: Wednesday, December 28, 2011 4:26 PM
To: [hidden email]
Subject: Re: chromatic aberration

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How are you measuring the aberration?  Beads?  Reflectance?

On 12/28/2011 2:46 PM, MODEL, MICHAEL wrote:

> Olympus. Their higher-NA objectives are fine
>
> -----Original Message-----
> From: Confocal Microscopy List [mailto:[hidden email]] On Behalf Of Martin Wessendorf
> Sent: Wednesday, December 28, 2011 3:25 PM
> To: [hidden email]
> Subject: Re: chromatic aberration
>
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>
> Hey, Mike--
>
> On 12/28/2011 2:01 PM, MODEL, MICHAEL wrote:
>
>> Both of our 10/0.4 planapo objectives have a bad longitudinal chromatic aberration between blue and far red (2.5 um axial shift with correct coverslip). Is this normal for low-power objectives?
>
> What manufacturer?  Not to trash any particular brand but I've seen
> problems that bad on 60x oil objectives from some makers and would
> expect a 10x objective to be even worse.
>
> Martin

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